The Human Genome Project and various new technologies linking disease phenotypes with cellular genotypes have ushered in a new era in life science research and personalized medicine. Post-genomic era research promises improved clinical diagnostics, better pharmaceutical products and individualized healthcare. Such research begins with asking a specific molecular question of multiple stored precious biologic solutions containing DNA, cDNA, RNA, protein, or other materials isolated from diseased or normal tissue. Such research and practice often require the precise handling of a large number of samples, preferably in an automated apparatus and contained in specialized containers.
At present, precious DNA and other precious liquid biologic samples used for such studies are typically maintained in aqueous form with solvents such as pure water or Tris-EDTA solutions. Such samples are typically stored in plastic containers such as microcentrifuge tubes or multi-well or multi-tube plates. These solutions are stored at temperatures of 4° C. or −20° C., with a small percentage at −80° C. or lower. Among many drawbacks of the current practice, contamination, evaporation, and lack of convenient inventory control are prominent.
A first problem is contamination. Each time a precious liquid biologic sample is needed, its container is thawed, the cap is opened, and a manually directed pipette is inserted to aspirate and transfer the desired amount of solution to a separate receptacle. Manual pipetting is prone to accidental placement of a contaminated pipette tip into a sample. Similarly, automated pipetting, which is typically done with 96-well or 384-well plates, requires prior removal of either a non-sealing plastic closure or an adhesive film to access the solution, which may be repeated many times for a given sample. While removing the seal, the samples may be aerosolized through vibration of the solution, which increases the risk of cross-contamination. This is especially true, for example in 96-well or 384-well plates, where the point of access for each individual sample is either contiguous or in close proximity to points of access for other individual samples. A single contamination event can lead to costly delay and repetition of experiments if detected, and if undetected can cause misinterpretation of experimental results.
A second problem is evaporation. The primary source of evaporation and concentration change is a lack of robust sealing of most microcentrifuge tubes, which permits the exchange of air saturated with precious liquid vapor and unsaturated air. Consequently, investigators often use samples whose precise concentration is unknown, which increases the rate of failed, invalid, non-reproducible, and/or un-interpretable results. Laboratories requiring greater quality control recheck the concentration of the samples prior to each use, a practice that is time consuming, expensive, and also wastes precious biologic materials.
A third problem is a lack of convenient inventory control. Since no convenient standard method exists to continuously track and maintain records of liquid sample availability, volume, and concentration in real-time, laboratory productivity suffers in numerous ways including: underutilization of samples already obtained by the laboratory but which have been lost in refrigerators or freezers; poor planning or avoidance of demanding experiments because it is too time consuming to determine if necessary samples are available in inventory; and inability to conveniently determine whether a proposed collaboration is feasible.
Any system for long term, contamination-free storage of precious liquids requires a contamination-free means for dispensing aliquots of the liquid. Furthermore, the nature of the experiments conducted using the liquids is such that aliquots ranging in volume from 1 to 20 or more microliters are required, with a dispensing precision of a few percent.
Therefore, a need exists for an apparatus and processes that overcome these limitations presently in the art and provide for the inexpensive storage, tracking, and dispensing of precious biologic solutions. Specifically, a need exists for a robust, reliable, and secure long-term storage and precision dispensing system for precious biologic solutions for use in life science research and molecular medicine.
While the reliable, efficient, contamination-free management of precious liquids is a particular problem in current biological investigations, similar problems exist in any area where precious liquids are managed. Examples of such areas include, but are not limited to, chemical reagent design and delivery, perfume design and manufacture, scent design and manufacture, food additive testing and design, drug design and manufacture, pigment design and manufacture, and others.
In the course of biological assays, investigators often require aliquots as small as 1 microliter to be dispensed. With any practical size of dispensing pipette tip, it is not possible to detach a drop smaller than about 5 μl from the tip unless it is ejected by air pressure from within or outside of the pipette tip, or unless it is transferred to the surface of the receiving container by touching. If the precious liquid is kept contamination-free by being permanently stored in the dispensing device, as opposed to being withdrawn through an inserted pipette; ejection using air pressure from behind the liquid is relatively complex and expensive. A simpler ejection method is desired. Furthermore, contamination control requires that the tip of the storage and dispensing device never comes into close proximity with foreign liquids such as may be in a receiving container, so the touch-means of transferring small drops would not typically be acceptable.
The non-intrusive method of dispensing liquids from such a storage cartridge with a slidable piston, such as an injection syringe, is by mechanically depressing the piston, thereby expelling the liquid through an orifice in the cartridge. A precise volume may be dispensed by accurately controlling the mechanical depression of the piston.
However, there is always some degree of compliance in the construction of the cartridge, piston and piston seal. Therefore, when the piston depression force is relaxed, the liquid is sucked back from the tip of the orifice into the storage chamber to an extent determined by the reduction of piston depression force and the compliance of the design. Furthermore, when first inserting the cartridge into a mechanical depressing device, the contact between the depressing device and the cartridge piston may not be intimate, so an unknown gap between the depressing device and the cartridge piston is introduced.
This suck-back effect and this lack of intimate contact introduce an unknown offset between the amount of mechanical depression of the piston and the volume of liquid expelled. The offset is only a factor in the initial aliquot dispensed; subsequent aliquots have a known starting state providing that the pressure on the piston is not relaxed between aliquots.
In biological investigation it is often necessary to dispense only one microdrop of liquid of known volume from a delivery device. The known starting condition must therefore be established by depressing the piston by a distance sufficient to ensure that the liquid has reached the tip of the orifice. Establishing that the liquid has reached the tip of the orifice is conventionally done, for example in medical injections, by depressing the piston until liquid is discharged from the orifice, wasting the expelled liquid. However, in genomic research the value of precious liquids is often too high and available quantity too small to tolerate such waste, and in addition provision for contamination-free storage and disposal of such waste would be expensive and time-consuming. There is a need in the art to provide methods and devices for precise waste-free liquid dispensing.